This invention relates to a diaphragm for use in electro-acoustic transducer such as a loud speaker, microphone or the like.
Diaphragms for use in electro-acoustic transducers such as a speaker or a microphone generally must satisfy the following requirements:
(1) light in weight, PA1 (2) high rigidity (Young's modulus E) and moderate inner loss (tan .delta.) PA1 (3) a high ratio between the Young's modulus E and the density .rho., that is, specific modulus E/.rho. or great sound propagation velocity .sqroot.E/.rho.. PA1 (a) those mainly composed of natural fibers such as plant fibers, animal fibers and mineral fiber, PA1 (b) the natural fibers as described above impregnated with thermosetting resin such as phenol resin or epoxy resin, PA1 (c) plastic sheet made of polypropylene, polyethylene terephthalate, etc. PA1 (d) metal member such as made of aluminum or titanium.
The conventional materials for forming these diaphragms include:
Among them, the diaphragms made of the natural fibers (a) as the main component can provide a flat frequency characteristic owing to their large inner loss tan .delta. but they are highly hygroscopic and cause fluctuations in the acoustic tone leading to degradation in the tone by way of aging.
Further, those natural fibers impregnated with a thermosetting resin such as phenol or epoxy resin as described in paragraph (b) above have a low inner loss tan .delta. and high density .rho.. Accordingly, the plate thickness has to be reduced in order to decrease the weight of the diaphragm, which results in a defect of peak dip in the frequency characteristic. Further, although the diaphragm made of plastic sheets such as of polypropylene or polyethylene terephthalate as decribed in (c) above is excellent in water proofness, they are liable to cause deformation at a high temperature atmosphere of about 100.degree. C. and require an increased cost.
Furthermore, although the diaphragm shaped by using metal members of aluminum or titanium as described in (d) above has a great Young's modulus E since the inner loss tan .delta. is small, it is difficult to damp the resonance at a higher frequency region, the ductility of the material is limited to worsen the workability and the cost is extremely expensive.
As described above, the materials (a)-(d) as described above, are not suitable as the material for forming the diaphragms for use in electro-acoustic transducers.